1. Field of the Invention
This invention relates to a surface fastener integrally molded continuously of thermoplastic resin by continuous injection or extrusion and composed of a substrate sheet and a multiplicity of engaging elements standing on a front surface of the substrate sheet, and a method and apparatus for continuously manufacturing the molded surface fastener. More particularly the invention relates to a molded surface fastener having a unique shape and excellent in engaging rate and engaging strength, and a method and apparatus for continuously manufacturing the molded surface fastener.
2. Description of the Related Art
Conventionally, an engaging member in which female surface fastener having a multiplicity of loops on the front surface of a substrate sheet, and male surface fasteners having on the front surface of a substrate sheet a multiplicity of engaging elements engageable with the loops are engaged by pressing, are already known. In recent years, application of such surface fasteners is on the increase from connectors for daily goods to connectors for various kinds of industrial materials.
Although the surface fastener having a multiplicity of loops on the front surface of a substrate sheet is yet made of woven or knit fabric or non-woven cloth obtained by weaving or knitting fiber threads with no large variation as compared to the conventional surface fastener, attempts have been made to improve engaging elements of the surface fastener in order to cope with the above-mentioned various uses, and at the same time, considerations have been made also with respect to the cost of production.
Further, the use of the above-mentioned surface fasteners is on the rise also for underwear such as diaper; therefore, the engaging elements for this use are required to have adequate engaging strength, adequate softness and less itchy touch. For this purpose, it is additionally cherished that the size of the engaging elements are reduced to a minimum. Especially since disposable daily goods such as paper diaper should be inexpensive, fiber woven or knit surface fasteners tend to be avoided to lowe the price as much as possible.
On the other hand, the shapes of the conventional engaging elements are chiefly divided into three shapes: the hook-shape engaging element having a hook-shape engaging head curving in an arc downwardly from the upper end of a stem standing on the front surface of the substrate sheet; the so-called mushroom-shape engaging element having an umbrella-shape engaging head bulging in all directions and upwardly from the upper end of a stem standing on the front surface of the substrate sheet; and the palm-tree-shape engaging element having a palm-tree-shape hook engaging head projecting from the upper end of a stem standing on the front surface of the substrate sheet. Of course, various modifications have been suggested to improve these three types of engaging elements individually.
These three types of engaging elements are remarkably different in engaging characteristic from one another as follows. The hook-shape engaging head of the hook-shape engaging element tends to deform and catches a companion loop almost at the same position, while the umbrella-shape engaging head of the mushroom-shape engaging element is hard to deform and is engaged by a plurality of companion loops crosswise in various directions. Therefore, the hook-shape engaging element has generally less engaging strength than the mushroom-shaped engaging element. However, the mushroom-shaped engaging element tends to be encountered with a so-called hanging phenomenon and also tends to damage itself or the companion loops during repeated use, thus it is disadvantageous in this respect as compared to the hook-shape engaging element. Regarding the rate of engagement with the companion loops, the mushroom-shape engaging element is superior to the hook-shape engaging element since the mushroom-shape engaging elememt can engage in any direction, and is easier to engage small loops. In the meantime, the engaging characteristic of the palm-tree-shape engaging element may be described as a compromise between that of the mushroom-shaped engaging element and that of the hook-shape engaging element.
For the above-mentioned reasons, surface fasteners having mushroom-shape engaging elements are increasingly used as fasteners for industrial materials, interior ornaments and daily goods, which require adequate engaging strength and are used relatively less repeatedly. This mushroom-type surface fastener is exemplified by woven or knit fiber surface fastener disclosed in, for example, U.S. Pat. Nos. 3,191,255 and 4,846,815 and a molded synthetic resin surface fastener disclosed in, for example, U.S. Pat. Nos. 3,718,725 and 5,077,870 and International Publication No. W094/23610.
A compromise engaging element between the hook-shape engaging element and the mushroom-shape engaging element is disclosed in Japanese Patent Publication No. Sho 63-66524. According to this Publication, the engaging element is made of monofilament composed of monofilamentary stem standing in an inclined posture or a substantially upright posture from the knit cloth surface, and a substantially egg-shape engaging head integral with and projecting from the stem horizontally or diagonally upwardly. The engaging characteristic of this surface fastener is a compromise between the hook-type fiber surface fastener and the mushroom-type fiber surface fastener. Namely, this surface fastener is easy to peel like the hook-type surface fastener and has adequate engaging strength like the mushroom-type surface fastener and can secure adequate resistance against repeated use.
The fiber surface fastener disclosed in, for example, U.S. Pat. Nos. 3,191,255 and 4,846,815 has adequate softness because of its substance. However, this fiber surface fastener requires many processing steps, which is low in productivity and high in cost.
The surface fastener dislcosed in Japanese Patent Publication No. Sho 63-66524 is composed of a fiber knit cloth like the foregoing surface fasteners, and it has also poor productivity and it has limit in lowering of its price. Further, since the egg-shape engaging head formed at an upper end of the engaging element of the surface fastener extends in parallel to the substrate cloth surface or a tip end of the engaging head faces diagonally upwardly, the stem is inclined further in the direction of its inclination when the surface fastener is pressed by the companion surface fastener. Therefore, most of the engaging heads face diagonally upwardly and as a result, a predetermined rate of engagement is hard to achieve. Also upon completion of engagement with the companion loops, the engaging element is less resistant against separation and can hence be separated very easily since the engaging element is made of monofilament so that they are too flexible and the engaging head has the above-described shape.
On the other hand, the molded synthetic resin surface fastener disclosed in, for example, U.S. Pat. Nos. 3,718,725 and 5,077,870 and International Publication No. W094/23610 can be efficiently manufactured by a continuous process and is therefore low in price. Generally, however, this type surface fastener is large in rigidness and inevitably gives a hard touch, particularly a very itchy touch when the upper end of the engaging element comes into contact with the user's skin. Therefore the surface fasteners of this conventional type are not suitable for daily goods such as underwear, and they are used msotly as connectors for industrial materials.